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The OpenCV (Open Source Computer Vision) library provided the implementations for many of the methods explained in this module. Detailed explanations of the functionality are available on the OpenCV website.

Why use color isolation?

Many computer vision methods exist for feature detection (such as detecting faces or characters in an image). We wanted the possibility to track multiple types of objects with our virtual theremin. Feature detection does not allow for this flexibility. We also needed our object recognition to be fast in order to drive real time audio. Feature detection algorithms work, but are known to be a bit slow. In order to address these concerns, we opted to use color to track objects. When the user launches our program, the user must select the object they wish to track. The color of this object is stored by the program. Every future frame retrieved by the webcam is scanned for all pixels within range of that color, allowing for the isolation of the object after a few steps.

Color spaces


Cameras operate in the RGB color space. In the RGB color space, images store three channels of information: red, green, and blue. For each channel, 8 bits of data is stored. RGB images use additive color mixing: zeros in all channels represents black and 255 in each channel represents white. Although this color space is easy to use, highlight and shadow affect RGB values. Therefore, tracking using RGB values is not a realistic option to track a constant color.


Our virtual theremin first converts RGB to HSV. HSV is an alternative color space that uses three different channels of information: Hue, Saturation, and Value. The HSV color space represents colors according to the figure below. Unlike RGB, highlight and shadow do not cause changes in hue values. Therefore, it is possible to track an object in variable lighting conditions using HSV. The conversion to HSV from RGB is as follows:

HSV Equations HSV Equations HSV Equations
HSV Color Space
The HSV Color Space

If the above formula results in H less than 0, it is converted to H+360.

Object detection

Gaussian blur

Before any detection is attempted, a slight blur is applied to the image using a Gaussian kernel. This blur smoothes out any noise in the initial image. The blurred image is then converted to the HSV color space.

Original Image
Original Image
HSV Image
HSV Image
Original and HSV Images

Image thresholding

The user initially selects a point in the image. The HSV value at this point is used as the center color in the threshold range. Using the values set by the margin sliders, the HSV image is converted to a binary image by thresholding the HSV image to the specified range around the selected color.

Thresholded Image
Thresholded Image

Object isolation

Depending on the environment, the thresholding image may or may not contain other noise. The example photo was taken against a solid background of a different color. Therefore, there is no other noise visible in this image. However, in order to determine which portion of the thresholded image is our desired object, we assume that noise is present.

We first find all of the contours from the edges in the thresholded image. For each found contour, we compute the area enclosed. We assume that the contour enclosing the largest area is the desired object. Once this specific contour has been determined, we fit an ellipse to the contour. From this ellipse, we can determine the angle of the major axis and the position of the center. The isolated image, shown below, has this ellipse drawn in red around the contour shaded in blue.

Isolated Image
Isolated Image

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
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Source:  OpenStax, Virtual theremin. OpenStax CNX. Dec 18, 2013 Download for free at http://cnx.org/content/col11605/1.1
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